The present invention relates to turbomachinery, and more specifically, but not exclusively, relates to the control of clearance between an impeller and a shroud of a turbomachine.
It is often desirable to minimize clearance between the blade tips of an impeller rotating within a gas turbine engine and a surrounding blade tip shroud to reduce leakage of a working fluid around the blade tips. Frequently, blade clearance minimization is of particular interest for centrifugal compressor stages. One approach to blade clearance minimization has been to provide an abradable coating on the shroud surface that may be rubbed away by blade contact to create a reduced clearance customized to the particular blade/shroud arrangement. Unfortunately, this type of coating may not be suitable for some gas turbine engine applications--especially those where a smooth shroud surface is desired. Indeed, rough, uneven surfaces commonly associated with abradable coatings often adversely impact engine performance. Moreover, it is sometimes desirable to dynamically change clearance during operation, which is not accommodated by such coatings.
Consequently, several actuation schemes have arisen to provide for blade tip clearance adjustment during engine operation. Unfortunately, these systems often include complicated linkages, contribute significant weight, and/or require a significant amount of power to operate. Thus, there continues to be a demand for advancements in blade clearance technology.